178 THE OLIVER PLOW BOOK 



power. AC then represents the line of draft which is 

 angular to EC, the force which should act to pull the 

 plow forward in the perfect line of draft, if the operator 

 desires to plow properly. 



According to the laws of physics, AB and AE consti- 

 tute a parallelogram of force, hence the magnitude of 

 the forces AB and AE is proportional to their length. 

 In this diagram the proportion is 14 to 4. 



Assuming it requires 540 pounds to operate the plow, 

 this means then that 420 pounds are required to pull 

 the plow straight ahead and 120 pounds to overcome 

 the side draft. It is perfectly plain then that the tractor 

 which is hitched to one side of the center line of draft in 

 this case is required to withstand a tortional stress of 120 

 pounds. It is also apparent that as the line BC is 

 placed closer to EA the proportion of forces becomes more 

 evenly divided. 



For example, if the hitch between the tractor and 

 plow were shortened so that ABCE would form a square, 

 then force AE would be equal to force AB; that is, the 

 side draft would be increased to one half of 540 pounds. 

 In actual practice with such a hitch as this it would 

 require more than 540 pounds to pull the plow, because 

 the tractor would be operating at a tremendous dis- 

 advantage on account of the additional force tending to 

 pull the rear wheels of the tractor toward the line of 

 draft (which as has been explained previously in this 

 chapter will always straighten itself regardless of what 

 forces may be acting against it). Hence, it is evident 

 that the hitch on the tractor must be in a straight line 

 from the center of weight to the center of hitch on the 

 tractor if the minimum of power is required to pull the 

 plow. 



